Cabinet sealant is used in the manufacture of appliances such as refrigerators, freezers and refrigerated vending machines. The sealant is foamed over all the holes, gaps, and spaces of the appliance housing, which typically comprises ABS plastic or painted metal, prior to filling the housing with urethane based insulation. The primary purpose of the sealant is to prevent the insulation from leaking out during the filling process. Further, the cabinet sealant must withstand temperatures ranging from about 60.degree. C. (140.degree. F.) to about 82.degree. C. (180.degree. F.) and gas pressures associated with the urethane insulation filling and foaming processes. It is difficult to cover all the holes and gaps in the appliance housing without also unintentionally over-spraying the foam onto the exterior of the appliance at visible locations. Accordingly, it is critical that the cabinet sealant be cleanly strippable from the appliance housing in order to easily remove the over-sprayed foam.
Other methods of sealing the appliance housing prior to filling with insulation include pliable permagum/duragum based mastics, masking tape, and foam/fiberglass pads coated with a pressure sensitive adhesive. Since these alternative methods are slow, costly and labor intensive, the method of sealing the appliance housing with a foamed sealant is far preferred.
Block copolymer based cabinet sealant, particularly S-EB-S based have been used extensively. Other block copolymers such as S-B-S and S-I-S are typically used to a lesser degree, as block copolymers having an unsaturated midblock tend to exhibit poor thermal stability. Such block copolymers are compounded with diluents such as oil and wax.
Amorphous polyalphaolefins (APAO's) are available in low viscosity versions. However, most compositions are not cleanly strippable from ABS plastic or painted metal due at least in part to the pressure sensitive nature of such compositions. To compensate for this disadvantage, formulators have attempted to dilute higher molecular weight APAO's with diluents such as oil and/or wax to lower the viscosity and reduce adhesion. These attempts have been unsuccessful in that the mixture once foamed lacks sufficient cohesive strength to be cleanly strippable. Accordingly, the use of APAO based compositions requires the use of solvent to remove the overspray.
Foams for disposable articles are often required to exhibit somewhat different properties than that of a foamable cabinet sealant. For example, U.S. Pat. Nos. 5,342,858 and 5,389,168 issued to Litchholt et al. are directed to an elastomeric adhesive foam comprising an A-B-A block copolymrer; an aromatic modified hydrocarbon resin; and optionally a processing oil. Columns 1 and 2 of the U.S. Pat. No. 5,342,858 patent discusses in detail the advantages of forming elastomeric foams on-line as well as the shortcomings of the prior art elastomeric adhesive compositions. Exemplified are adhesive compositions comprising 45 wt-% of an S-I-S block copolymer, 40 wt-% tackifying resin, and 15 wt-% oil having viscosities ranging from 11,125 cP to 34,000 cP at 163.degree. C. (325.degree. F.). Although the compositions of Litchholt represent an improvement in processability with respect to the prior art, the examples that were foamed, Examples 1 and 2 employ application temperatures of 163.degree. C. (325.degree. F.) and 191.degree. C. (375.degree. F.), respectively. High application temperatures are detrimental for several reasons. For example, high application temperatures can cause heat deformation of heat sensitive substrates, particularly of polyolefin films. Since thermoplastic compositions tend to have good insulating properties it is very difficult to sufficiently cool a mass of molten hot melt adhesive. This is especially true since gases tend to be even worse conductors of heat than thermoplastics, a foamed thermoplastic composition is even more difficult to cool. Also, poor foam quality due to remelting of the foam cell walls, and reduced line speeds due to the extended cooling times needed to sufficiently cool the foam can also result.
U.S. Pat. Nos. 5,369,136 and 5,407,965 issued to Park et al. teach an ethylenic polymer foam structure comprising an ethylenic polymer material. This reference is directed toward conventional extrusion foaming processes employing very viscous polymer in combination with a blowing or nucleating agent. Exemplified are ethylenic polymers having a low melt index ranging from 0.57 dg/min to 5.17 dg/min. Such polymers are too high in viscosity to be applied by hot melt adhesive foam applicators.
Therefore, industry would find advantage in a foamable composition comprising a low viscosity thermoplastic material exhibiting good thermal stability that may be applied at low application temperatures. The present inventors have found that certain metallocene polyolefins based compositions find utility as foamable cabinet sealant, in the manufacture of disposable articles for creating in-line foam layers, as well as for a variety of other uses.